import hashlib as hasher

class Block:
        def __init__(self, index, timestamp, data, previous_hash):
                self.index = index
                self.timestamp = timestamp
                self.data = data
                self.previous_hash = previous_hash
                self.hash = self.hash_block()

        def hash_block(self):
                sha = hasher.sha256()
                sha.update(str(self.index) +
                           str(self.timestamp) +
                           str(self.data) +
                           str(self.previous_hash))
                return sha.hexdigest()


import datetime as date


def create_genesis_block():
        # Manually construct a block with
        # index zero and arbitrary previous hash
        return Block(0, date.datetime.now(), "Genesis Block", "0")


def next_block(last_block):
        this_index = last_block.index + 1
        this_timestamp = date.datetime.now()
        this_data = "Hey! I'm block " + str(this_index)
        this_hash = last_block.hash
        return Block(this_index, this_timestamp, this_data, this_hash)


# Create the blockchain and add the genesis block
blockchain = [create_genesis_block()]
previous_block = blockchain[0]

# How many blocks should we add to the chain
# after the genesis block
num_of_blocks_to_add = 20

# Add blocks to the chain
for i in range(0, num_of_blocks_to_add):
        block_to_add = next_block(previous_block)
        blockchain.append(block_to_add)
        previous_block = block_to_add
        # Tell everyone about it!
        print "Block #{} has been added to the blockchain!".format(block_to_add.index)
        print "Hash: {}\n".format(block_to_add.hash)
